Fluidized-bed system for patenting steel wire



Aug. 25, 1970 ET AL 3,525,507

FLUIDIZED-BED SYSTEM FOR PATENTING STEEL WIRE Filed Oct. 16, 1967 5Sheets-Sheet 1 3o 40 50 6o 80 0o 11sec] FIG I H. Geipel E.. Fb'rsfer W.Heinemann INVENTORS.

WA R088 Attorney Aug. 25, 1970 H, q pE ET AL 3,525,507

FLUIDIZED-BED SYSTEM FOR PATENTING STEEL WIRE Filed Oct. 16. 1967 3Sheets-Sheet 2 INVENTORS HANS GE/Pfl. :cxemnar Fozsma warn/0 HE'INEMANJVKol 'A rramvrr Aug. 25, 1970 H. IGEIPEL ET AL FLUIDIZED-BED. SYSTEM FORPATENTING STEEL WIRE Filed Oct. 16. 1967 3 Sheets-Sheet 5 FIG. 3

1N'VENTORS HANS GE/PEL, sake-W420? #025724 wa e/Ea I/E/NEMAN/V I. 6R9 Il ,4 Tran/v45? United States Patent 3,525,507 FLUIDIZED-BED SYSTEM FORPATENTING STEEL WIRE Hans Geipel, Oberhausen-Sterkrade, EckehardtForster,

Oberhausen, and Wilfried Heinemanm Duisbur'g, Germany, assignors toHuttenwerk Oberhausen AG, Oberhausen, Germany, a corporation of GermanyFiled Oct. 16, 1967, Ser. No. 675,522 Claims priority, applicationGermany, Oct. 25, 1966, H 60,847, H 60,848 Int. Cl. C21d 9/56 US. Cl.266-3 6 Claims ABSTRACT OF THE DISCLOSURE Austenitic steel wire, havinga starting temperature above the transformation point Ac is passedthrough a fluidized bed of solid ceramic particles entrained by a streamof carrier gas, the gas temperature and/or the residence time in the bedbeing so chosen that the wire emerging from the bed has a temperature(around 550 C.) in the range in which transformation to sorbite occursbut above the level (around 500 C.) below which the formation of bainitewould take place.

Our present invention relates to a plan for patenting steel wire.

The term patenting is understood in the wire-making art as identifying atreatment of hot steel wire of medium or high carbon content,preparatory to a drawing of the wire to final size, whereby thetemperature of the wire is reduced at a controlled rate from a levelabove the critical point Ac (transformation of ferrite to austenite) toa range in which austenite is transformed into pearlite. This cooling isconventionally carried out in air or in a fused bath, such as moltenlead.

In order to satisfy the usual requirements of ductility, flexibility andtensile as well as torsional strength, the wire so treated should have apredominantly sorbitic crystal structure. Sorbite is a fine-grainedvariant of pearlite and comes into existence upon transformation ofaustenitic steel at a temperature of approximately 550 C. If thetransformation occurs at a lower level, generally below 500 C., thepearlite crystals are still smaller and form a structure known asbainite. This structure is consideraby harder than the sorbite andunsuitable for drawing. If, on the other hand, transformation is allowedto occur at temperatures above the level of substantially 550 C., thepearlite becomes progressively coarser as its crystals are surrounded bya ferrite skeleton; such a wire, typically obtained by patenting in air,has good ductility and torsional strength but does not withstand flexureas well as does wire transformed in a range of about 500 to 550 C.

The general object of our invention is to provide means for so cooling asteel wire, previously heated above the critical range, that the desiredsorbitic structure is invariably obtained in a rapid and economicalmanner with substantial exclusion of bainite.

A more particular object of this invention is to provide a treatment ofthis type which can be applied directly to wire coming hot from arolling mill.

In accordance with our present invention, a hot wire of austenitic steelis continuously passed through a cooling medium of the fluidized-bedtype, i.e. a stream of carrier gas with entrained solid particles suchas ceramic granules of elevated heat-transfer coefiicient (preferablybetween about 500 and 1000 Cal./m. /hr. C.) The particles may consist,for example, of magnesia and may range between 0.03 and 0.15 mm. indiameter, with a bulk weight of 1.5 to g./cm. Hydrogen, carbon mon-3,525,507. Patented Aug. 25, 1970 oxide or other relatively inert gasesconventionally used in metallurgical processes may serve as the carrierfluid. Though the temperature of the cooling medium (solid particles andcarrier gas) may be well below the bainiteformation level of about 500C., transformation is completed above that level because the wire is ledout of the fluidized bed in a state of incipient transformation beforeits temperature falls below the 500 C. mark. It will be understood thatthe exact temperature range to be observed for optimum results variessomewhat with the composition of the steel and can be determined fromavailable handbooks.

We have found that the treatment of wire by our present method resultsin a sorbitic structure comparable to that realizable, albeit atsubstantially lower production rates, with a bath of molten lead.Moreover, the treatment according to our invention is faster thanpatenting in air and tends to suppress the formation of the ferriteskeleton usually associated with air cooling.

After the wire has emerged from the fluidized bed, transformationproceeds to completion under substantially isothermic conditions, i.e.without the use of a cooling medium other than the surroundingatmosphere. To retard the cooling at this stage it is, however,desirable to shield the emerging wire by sheet-metal plates or the likereflecting its thermal radiation. The final cooling, subsequent totransformation, may also take place in air.

In order to stabilize thetemperature of the emerging Wire within thedesired range of approximately 500 to 550 C., we prefer to measure thattemperature and to compare it with a predetermined value to compensatefor deviations therefrom by a corrective adjustment of the bedtemperature and/ or of the residence time of the wire in the fluidizedbed. To control the temperature of the cooling medium, we prefer toremove particles continuously from the bed and to let them pass througha cooling chamber before returning them to the bed; this recirculationof the particles is best accomplished with the aid of a flow of carriergas which may itself be recirculated.

A plant suitable for carrying out the aforedescribed method comprises aconveyor, preferably in the form of an apertured belt, passing through achannel together with the stream of carrier gas and entrained solidparticles; the discharge end of the channel is provided with a gatethrough which the cooled wire may emerge while the particles areretained and form a nearly stationary accumulation around the exitingwire. The hot incoming wire may be deposited on the conveyor in asuccession of loops, advantageously with the aid of a transverselyoscillating dispenser as disclosed and claimed in our commonly ownedapplication Ser. No. 675,405 filed on even date herewith under the titleMethod of and Means for Cooling Wire.

The invention will now be described in greater detail with reference tothe accompanying drawing in which:

FIG. 1 is a transformation diagram showing the conversion of austeniticsteel to sorbite by conventional means and by the process of ourinvention;

FIG. 2 is a somewhat diagrammatic side-elevational view of a plant forcarrying out the process; and

FIG. 3 is a fragmentary view similar to FIG. 2, showing a modification.

In FIG. 1 we have shown at A and B the boundaries of theaustenite/pearlite transformation range for a typical steel wire of 5.5mm. diameter, made from unalloyed steel with a carbon content of 0.5%.Graph e represents an idealized process whereby the wire is rapidlycooled, from a starting temperature of 860 C., to a level of 550 C.which it reaches after 1 /2 seconds and where the graph intersects theboundary curve A of the transformation range. After a further intervalof about 18 /2 seconds, with gradual cooling to a point at or about 500C., the transformation to sorbite would be completed without theformation of appreciable quantities of bainite. Such an idealizedcooling process, e.g. with quenching in water, would be difficult torealize because of the problems of temperature control and appears to beimpractical for any but the thinnest wires.

It is widely assumed, even if not established by incontrovertible proof,that the qualities of steel wire especially in regard to fiexure areimproved by an approximation of the conditions represented by graph e.This may be accomplished, to a certain extent, by the use of a batch ofmolten lead (graph a) which, in order to avoid the formation of bainite,should be maintained at a temperature of about 500 C. so that the curveapproaches this level asymptotically; this type of treatment, completedafter 20 seconds, does not lend itself to the processing of hot wirecoming at relatively high speed from a rolling mill. Conventional aircooling (graph d) takes even longer and leads to incipienttransformation at a temperature close to 700 C., with resultingformation of a large-grain ferrite structure in the pearlite.

The patenting of wire in accordance with our present invention isrepresented by graphs b and 0. Graph b illustrates the cooling byceramic granules of the aforedescribed type having a heat-transfercoefficient oc=600 Cal./m. /hr./ C. as compared with a value 01:1180 forthe lead bath of graph a. Graph c applies to ceramic particles witha=850. The particle temperature is maintained well below 500 C., yetcontact between the particle stream and the wire is terminated at apoint p or q, thus after 8 or 6 seconds, respectively, when the wiretemperature drops to a level of 520 C. The treatment then continuessubstantially isothermally for a further period of approximately 20seconds, to a point r well beyond the intersection of graphs b and cwith curve B, whereupon final cooling proceeds in the open air (withoutany thermal shielding) as indicated by the joint portions b, c of thetwo graphs.

Reference will now be made to FIG. 2 for a description of a plant inwhich the process described in connection with FIG. 1 can be performed.The plant comprises a fluidized bed 1 confined within a tunnel 24,forming an elongated flow channel, to the vicinity of the upper run ofan endless conveyor belt 2 which is continuously driven by a motor 15 sothat a hot wire 3 deposited thereon is transported on a downwardlysloping path from right to left. Wire 3 passes through a guide tube 4and a continuously rotating dispenser arm 25, driven by a motor 26,whose rotation forms the wire into a succession of loops deposited onthe conveyor 2; the dispenser arm 25 may be subject to continuoustransverse oscillations at a frequency related to the loop-depositionrate, as described in our above-identified copending application of evendate, for the purpose of insuring optimum distribution of the loops overthe available conveyor surface. Belt 2, designed as a wire screen orother apertured member, transports the loops through a gate 8 at thedischarge end of the channel, this gate being here shown as a simpleshutter having a slot for the passage of the wire loops; a moreelaborate gate, designed to prevent the loss of solid particles throughthe exit slot, has been disclosed in our concurrently filed and commonlyowned application Ser. No. 675,426 entitled Fluidized Bed, nowabandoned. A perforated base 27 within tunnel 24 forms the lowerboundary of bed 1 and is connected to outlets of a manifold 10 throughwhich a carrier gas, as indicated by the arrows, is passed atlongitudinally spaced locations by way of the interstices of belt 2 intothe space thereabove. The branch conduits of manifold 10 containrespective valves 9 for controlling the amount of gas thus introduced. Afurther valve 28 controls the input from a compressor or otherhigh-pressure source, not shown, whereas two other valves 29, 30determine the proportion in which a portion of the gas is branched offinto a conduit 5 into which opens an outlet of a cooling chamber 6, thelatter containing a coil 22 traversed by a coolant. Conduit 5 opens intothe tunnel 24in the vicinity of the housing 23 of the dispenser arm 25.

Solid particles entrained by the gas stream accumulate in a pile justahead of the shutter 8 where the tunnel 24 is formed with a dischargeport 7 for these particles. A similar accumulation is formed at theentrance end of the tunnel by means of a stationary plate 31 underlyingthe upper run of conveyor belt 2 beneath an inlet branch 32 of conduit5. Port 7 communicates with a further conduit 33 which leads to the topof cooling chamber 6 and which may include means, such as a pump 34, topromote the return of solid particles from the discharge end of tunnel24 to the cooler. Another conduit 16, provided with a control valve 35,serves as a suction line to exhaust particles from the vicinity ofshutter 8 to a separator 18 when they are returned to cooled 6 via apipe 21; the spent carrier gas drawn off by line 16, and by a "branch 36thereof extending from the entrance end of the channel, is removed by apump 17 into a conduit 19 whence it may be discharged by way of a valve37 to the atmosphere or to the low-pressure side of the compressordelivering fresh gas to valve 28. A bypass 20, controlled by a valve 38,enables the recirculation of some or all of the gas to manifold 10.

In accordance with an important feature of our invention, a temperaturefeeler 11 just beyond shutter 8 senses the temperature of the emergingwire loops and feeds this information to a comparator 13 receiving areference signal from a storage device 12 adjusted to the desired exittemperature (e.g. 520 C.). Comparator 13 sets a controller 14 which, ifnecessary, adjusts the speed of motor 15 to vary the residence time ofthe wire in the fluidized bed 1 in a manner compensating for anydeviations of its exit temperature from the preset reference value.

Dispensing arm 25 is, of course, representative of any convenient typeof loop depositor including, for example, devices of the type shown inUS. Pats. Nos. 3,056,433 and Re. 26,052.

The -wire 3 exiting from gate 8, thermally shielded against excessiveradiant-heat losses by a tube 39 forming an extension of tunnel 24,continues on conveyor 2 in the ambient atmosphere until itstransformation has been completed (point r in FIG. 1). Thereafter, itmay be aircooled more rapidly outside the tube 39, by the same oranother conveyor or without any conveyor at all, to room temperature.

In FIG. 3, where elements corresponding to those of FIG. 2 have beendesignated by the same reference numerals with addition of a prime mark,we have shown the temperature sensor 11 disposed ahead of shutter 8'.Sensor 11' ascertains the exit temperature of the wire in terms of thetemperature of the fluidized bed 1 at the discharge end of tunnel 24'and, as before, communicates this information to a controller 14'; theoutput of this controller, in contradistinction to the previousembodiment, sets a servomotor 40 which adjusts a valve 41 to regulatethe amount of cooling fluid passing through coil 22 of chamber 6'. Thesystem operates otherwise in the same manner as the arrangement of FIG.2. Naturally, the control systems 11, 11 shown in FIGS. 2 and 3 couldalso be combined in a single plant.

We claim:

1. A plant for patenting steel wire, comprising a continuously movableapertured conveyor belt; dispenser means for continuously depositingupon said conveyor belt a length of austenitic wire heated above thecritical temperature range; circulating means for blowing along saidconveyor belt a gas stream with entrained solid particles; channel meansfor confining said gas stream to the vicinity of said conveyor means,said channel means including a base below said belt having perforationsspaced in the direction of belt motion and connected to said circulationmeans for admitting carrier gas through the apertures of said belt intothe space thereabove; gate means at a discharge end of said channelmeans for forming a terminal accumulation of said particles throughwhich said wire passes on emerging from said gas stream; and controlmeans for so regulating at least one operating parameter of the plant asto maintain the temperature of the emerging wire substantially at alevel of incipient transformation of the austenite to sorbitic pearlitebut above a point below which substantial amounts of bainite would beformed.

2. A plant as defined in claim 1 wherein said control means comprisestemperature-sensing means at said discharge end and speed-regulatingmeans for said conveyor belt responsive to said temperature-sensingmeans.

3. A plant as defined in claim 1 wherein said control means comprisestemperature-sensing means at said discharge end andtemperature-regulating means for said particles responsive to saidtemperature-sensing means.

4. A plant as defined in claim 1 wherein said conveyor belt extendsgenerally horizontally with a downward slope toward said discharge end.

5. A plant as defined in claim 1, further comprising thermal shieldmeans beyond said discharge end for limiting heat radiation from theemerging wire to the surrounding atmosphere.

6. A plant as defined in claim 1 wherein said circulation means includesa suction line for drawing spent gas from said channel means, separatormeans in said suction line for removing entrained particles from saidspent gas, means for cooling particles removed from said separatormeans, and conduit means connected to a source of carrier gas underpressure for returning the cooled particles from said chamber to saidchannel means.

References Cited UNITED STATES PATENTS 3,181,977 5/1965 Sturgeon 2664 X3,252,693 15/1966 Nelson 2663 3,355,159 11/1967 Ayers 2663 3,390,8717/1968 McLean et a1. 2663 3,391,915 7/1968 Morgan 2663 20 I. SPENCEROVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner US. Cl.X.R.

